Referring to FIGS. 1-3, a first connecting piece 3 is generally used in the prior art to fix a first electrode tab 21 of an electrode assembly 2 to a first electrode terminal 11 of a cap plate 1, and the first connecting piece 3 is provided with a first fusing portion 33. When a high current flows through the first connecting piece 3, the first fusing portion 33 can be fused in time so as to quickly cut off the electrical connection between the first electrode tab 21 and the first electrode terminal 11, and prevent a thermal runaway of the secondary battery. However, the first electrode terminal connecting portion 31 and the first electrode tab connecting portion 32 of the first connecting piece 3 will be separated from each other and become two independent parts after the first fusing portion 33 is fused, and when the electrode assembly 2 is subjected to external impact and vibrates, the electrode assembly 2 will bring the first electrode tab connecting portion 32 to move up and down via the first electrode tab 21, the first electrode tab connecting portion 32 will easily contact the first electrode terminal connecting portion 31 to establish the electrical connection between the first electrode tab connecting portion 32 and the first electrode terminal connecting portion 31 again, thereby resulting in thermal runaway and causing explosion, so the first fusing portion 33 cannot function for safety protection.